Existing forms and effects of carbon on the surface structure and hardness of ZrTiAlV alloys with various Zr contents

Abstract

The existing forms and effects of carbon on the surface structure and hardness of ZrTiAlV alloys with various Zr contents were investigated in this study. Each sample of ZrTiAlV–C alloys with Zr content below 17.3at.% is composed of (TiZr)C compound, a few β phases, and matrix α phase. The Zr content in the compound increases with increased Zr content in alloys. At 17.3at.% Zr content, both ZrC and (TiZr)C compounds are simultaneously observed. Only ZrC compound in addition to solid solutions is observed when the Zr content exceeds 17.3at.%. Comparison of the XRD results of ZrTiAlV–C alloys with those of ZrTiAlV alloys shows that the addition of carbon to ZrTiAlV alloys can restrain the precipitation of Zr–Al compound. Microstructures show that the grain size of carbide in ZrTiAlV–C alloys decreases with increased Zr content. Hardness tests show that addition of carbon markedly affects the mechanical properties of ZrTiAlV alloys as the Zr content changes. The hardness of ZrTiAlV alloys with Zr content below 17.3at.% gradually increases. However, a rapid decrease is observed when the Zr content is 25.95at.%. Then, a plateau is observed when the Zr content ranges from 25.95at.% to 60.55at.%, and a rapid increase is observed when the Zr content is 69.2at.%. However, the curve of hardness vs. Zr content of ZrTiAlV–C alloys is characterized as a parabola. The maximum hardness of ZrTiAlV–C alloys is 53.9HRC when the Zr content is 43.25%. The maximum hardness increases by about 11% compared with the maximum hardness of ZrTiAlV alloys with various Zr contents. Otherwise, hardness tests also indicate that the strengthening effect of carbide on the β phase is better than that on the α phase.